1. Field of the Invention
This invention relates to air particle sampling cassettes and devices, and more particularly to a dual air particle sample cassette that enables one or more samples of air to be taken at a time by the same vacuum sources.
2. Description of the Related Art
Air sampling has become an important aspect of safety and health concerns due to the rise of the present day industrial economy. Additionally, certain health aspects of individuals are better addressed when the pollen and/or particulate count of the surrounding area is known.
With respect to industrial processes and the like, chemical processes are often used in industries that produce substances that are generally not found in nature. Many of these are toxic and must be monitored in order to prevent injury, sickness, disease, or even death in individuals that might be exposed to such substances. Some of these substances are very potent and act very quickly while others require longer periods of time in order to have their deleterious effect. By monitoring or sampling the air, quantitative evaluations can be made upon such substances in the air.
With respect to people who have allergies, the pollen, mold, dust, and other particulates becomes important as their health is directly (and usually adversely) affected by the increase in such substances. By providing means by which such particulates can be detected, an individual allergic (or a community thereof) is better prepared to address the environmental conditions.
Other uses and applications for air samplers and the information delivered by them arise in a variety of circumstances. Certain biological, botanical, and other endeavors may benefit from an understanding of the air quality in certain areas. To this extent and otherwise, air sampling systems have arisen in the art to provide means by which quantitative information regarding air quality can be obtained by direct sampling of the air.
As set forth in U.S. Pat. No. 5,693,895 issued to Baxter on Dec. 2, 1997 for a Versatile Airborne Particle Impaction Sampler, obtaining accurate samples of airborne particles such as fibers, pollen, mold spores, insect parts and other bioaerosols is necessary or desirable for a number of different purposes. Environmental professionals have a need to determine the presence and quantity of deleterious particles such as asbestos fibers in the air. Aero-biologists and allergists need to identify and quantify airborne pollen and mold spore concentrations for patient diagnosis. Epidemiologists are concerned with particles carrying bacteria, such as that responsible for Legionnaire's Disease, in air-conditioning systems and the like.
An increasing need for more versatile, convenient and effective apparatus for sampling airborne particles has developed in such areas as environmental air quality monitoring, fire and flood restoration, and industrial and occupational monitoring.
Filter sampling has long been used for particle and fiber analysis. Air is drawn through a micro porous filter of the sort marketed by Millipore, Nuclepore and other companies. The filter is then examined under a microscope to determine the type and concentration of particles trapped on the filter media.
While effective for some purposes, filter sampling requires long sampling times to obtain reliable detection limits. The large filter areas require slow, careful examination by the microscopist performing the analysis. Relatively large filter areas, typically about 385 to 900 mm2, are normally required to balance high sample flow rates, required velocity and resulting back pressures. Large particles such as pollen often do not remain attached to the filter, separating there from during transportation and handling. Further, special stains and refractive index liquids required to assist in particle identification are often incompatible with the filter media.
Slit or impact samplers, which direct air at relatively high velocity through a narrow rectangular slit against a tacky material, have a number of advantages over filter sampling. A sample sufficient for analysis can be obtained in minutes rather than hours, the area to be examined is much smaller (approximately 16 mm2) than the areas provided with filters and the tacky nature of the material used to collect the sample will retain large particles better than filters. Present slit type samplers are assembled in a housing containing a vacuum pump, a holder for a slide coated with a tacky material, such as a suitable grease, with a narrow rectangular slot in the housing adjacent to the tacky surface.
These devices can only be used in an upright or fixed position and cannot be easily used in confined or restricted spaces such as ventilation ducts because of their relatively large size. Electricity to power the vacuum pump must also be run to the sampling site, or a battery power source in the housing must be provided which further increases the bulk of the unit. These units are not weatherproof and are difficult to use in moist or exposed areas. Dust contamination can build up inside the case resulting in cross contamination of sample slides and will require regular and extensive cleaning between sample collection episodes. Further, slit geometry in prior collectors is such as to collect the undesired less than about 2 μm particles, making examination and analysis more difficult.
Upon completion of sampling, the slides must be removed from the sampling device, packaged and shipped for analysis. Users must have specialized knowledge of sampling, decontamination, shipping and analysis procedures. Still, the opportunity for contamination, either inadvertent or intentional, is great.
With patients in hospitals, allergic persons while sleeping, workers in confined environments, etc. often have need for sampling near their faces to determine their actual exposure to allergens, toxic materials, etc. The large sampling devices of the prior art are very inconvenient for such uses, in particular where the person is mobile, because of their lack of easy portability.
Prior attempts have been made in the art with respect to sample cells and cassettes for air sampling systems and otherwise. Brief descriptions of such prior attempts are set forth below. While the descriptions are believed to be accurate, no admission is made by them regarding their subject matter which is solely defined by the patent or reference involved.
Typical of prior particle collection devices are those described by Berger in U.S. Pat. No. 4,725,294 and Leith in U.S. Pat. No. 5,304,125. The Berger device uses a single, round nozzle that will produce a circular, gradually decreasing spot of collected particles that is much more difficult to analyze than a narrow line of particles and will tend to collect sub-micron particles that obscure the larger which are to be analyzed. Leith discloses a device using four spaced slits that are simple slots in a thin plate, which will not discriminate between larger particles of interest and sub-micron particles that are not of interest.
The Baxter U.S. Pat. No. 5,693,895 discloses a single collector having a slide that is supported by the bottom ledge of the cell base.
The Marple et al. U.S. Pat. No. 4,827,779 discloses a personal air sampling impactor having a single vacuum source, multiple inlets, and in a separate embodiment, separate collection surfaces on the impactor plate.
The Marple U.S. Pat. No. 4,133,202 teaches a single stage impactor for sampling breathable aerosol particles having a nozzle plate with multiple different sized nozzles for allowing different sized particles through and an impactor unit with a plurality of particle collecting surfaces.
The Basch et al. U.S. Pat. No. 5,553,507 shows an airborne particulate sampling monitor having multiple intakes, each with its own filter unit, and a single vacuum source. The Shih et al. U.S. Pat. No. 5,702,506 teaches an aerosol size selecting sampling device having multiple inlets with pre-filters and a single vacuum source.
Van Den Wildenberg U.S. Pat. No. 6,342,388 discloses an apparatus for collecting airborne bacteria through impaction having multiple inlets and a single vacuum source.
The Sugita et al. U.S. Pat. No. 6,565,638 discloses a device for collecting air-borne micro-organisms having multiple nozzle openings and a single vacuum source.
The Jordan, Sr. et al. U.S. Patent Application Publication No. 2003/0075048 discloses a particle collection unit for separating particulate matter from a gas flow having an adhesive collecting member.
The Brixius et al. U.S. Pat. No. 3,898,161 discloses an air filtration device having a color-coded filter. Refer to column 4, lines 10-12.
The Miller et al. U.S. Pat. No. Des. 422,071—illustrates a partitioned filter element.
The Ayers published international application no. WO 03/002981—teaches a device for collecting and measuring particulate matter from a stream of air using two or more inlets each being selective as to the size of the particle able to pass through the inlet.
Despite the development of prior devices, the art may still be improved by a dual or multiple inlet air particle sample cassette that provides convenient means by which air may be sampled.